1. Field of Invention
This invention relates to a method of identifying a contour line of an object to be detected by using an image pick-up device, for example, a television camera.
2. Description of the Prior Art
Among prior art, methods of calculating the values of characteristic parameters of an object from a television picture image (a multivalue picture image) may be mentioned a region method and a contour line detection method.
According to the region method, the picture image is divided into a plurality of partial image regions each having substantially the same brightness and then the object is identified by judging the continuity of the regions on the assumption that respective surfaces of the object has similar brightness.
Although this method is effective for an object constituted by planes, when curved surfaces present, the processing thereof is difficult. Moreover, since all picture image data are processed, the amount of data becomes excessive, thus making it difficult a high speed processing.
On the other hand, the contour line extraction method utilizes the edges of respective surfaces of the object and according to this method, the points of the picture image at which the brightness changes rapidly are extracted as the edges, and the edges are connected together to convert them into a line picture. This method contemplates detection of lines in the picture image so that when compared with the region method which detects the surfaces, the number of detection stops and the quantity of informations for investigating their continuity are small so that high speed processing can be made.
The steps of identifying a circular body with the contour line extraction method will be described with reference to FIGS. 1a through 1d. At first, an original picture image (shown in FIG. 1a) photographed with a television camera is differentiated along respective scanning lines to extract a contour candidate point at which the brightness changes rapidly. Then, picture elements near this point are similarly differentiated and a picture elements having the maximum differentiated value is taken as a point continuous to the contour candidate point. This processing is repeated many times to obtain continuous contour points (contour line candidate)(see FIG. 1c) and when these contour points are closed (see FIG. 1d) they are deemed as an object.
According to this prior art contour extraction method, tracing of the contour candidate points are rendered difficult by the following factors.
(1) blooming caused by metal luster (see FIG. 2a), PA1 (2) overlapping of object (see FIG. 2b), PA1 (3) vague or not clear image caused by rust, spoil, etc. of the object surfaces, PA1 (4) distortion of the picture image caused by electrical noise.
As a consequence, there is a defect that an actually presenting object would not be detected. Furthermore, identifying algorithm for solving these problems becomes complicated so that real time processing is almost impossible.